The present report is a study on the side effects experienced by the patients attending the Lithium Clinic of the Institute of Psychiatry, Government Rajaji Hospital, Madurai. Out of the 120 (M 78, F42) patients studied, 97 had side effects. The effects were examined in respect of their frequency, time of onset and course, their relation to one dose and serum levels of lithium and to the clinical response. The duration of therapy ranged from 3 months to 6 years.The most frequent side effects were tremors (26.6%) and polyuria (20.8%). The side effects occurred at varying periods from the onset of therapy. During the first 3 months, tremors, excess salivation, nausea and abdominal discomfort; weight gain, memory defects and polyuria, between 3 months and 1 year; and hypothyroidism, tardive dyskinesia, acne and hair fall beyond one year.